Papers by Keyword: Particle

Abstract: A micro-meso-macro finite element approach has been developed for simulating the macro-scale damage coupled deformation in a particulate polymer composite (PPC) based structure under tension. A damage model for the PPC structure was developed to define the debonding damage behavior of the structure. The computational results determined in our previous studies by using finite element meso-cell modeling technique were used as the input parameters of the damage model and definition of the constitutive behavior of PPC. A user-defined subroutine VUMAT describing the damage-coupled constitutive behaviour of PPC for defining the material properties of the finite elements for the structure was then built and incorporated into the ABAQUS finite element code. A case example has been given to demonstrate the proposed approach. The macroscale damage process in the simulated component was found to be reasonable.

Abstract: In examining particulate deposits in the pipes within a chemical vapor deposition (CVD) system, vibration diagnostics is compared and studied against ultrasonic diagnostics. The latter method involves pulsing the outer wall of pipes with an ultrasonic sensor and analyzing the resulting echo to observe particulate deposits inside pipes. Vibration diagnostics examines the existence of particulate deposits by analyzing the difference in the frequencies generated when a vibrator is adhered to the outer wall of pipes. With ultrasonic diagnostics, good test results were obtained only when particulate deposits were attached to the inner wall of the pipes. After some time, however, particulate deposits were not detected properly, as the ultrasonic wave failed to cross the fine gaps created between the inner wall of the pipe and the deposits. In conclusion, the vibration diagnostics is being expected as the effective method in monitoring the particulate deposits inside pipes in the CVD system where the desired behavior is reduced frequency along with the the particulate deposits in comparison to the case where the pipe is clean.

Abstract: Nano-sized metal particles have recently attracted considerable interest owing to their application potential. Such particles can be synthesized using physical and chemical methods. In this study, nano-sized noble metals were synthesized through the reaction of metal oxides by ultrasonic. This means that the chemical reactions which take place under conventional conditions can be accelerated by ultrasonic cavitations. In general, the chemical effects of ultrasonic irradiation fall into three areas: homogeneous sonochemical efffects of liquids, heterogeneous sonochemical effects of liquid-liquid or liquid-solid systems, and sonocatalytic effects. It has been proposed that liquid-liquid systems are used for the fabrication of nano-metal particles in the past. In this study, the fabrication of nano-metal particles and supported composites was investigated for the liquid-solid system from a viewpoint of economy and ecology. By choosing suitable conditions, it is reasonable to expect that these simple ultrasonic processes can be extended to obtain nano-sized metal particles. Thus applications by using these reactions were investigated to prepare the nano-sized metal particle supported materials, and mechanisms were investigated.

Abstract: Unagglomerated α-Al2O3 powders of 100 to 200nm were synthesized by combustion spray pyrolysis with droplet filtration. The ignition conditions of the oxidizer and fuel were well elucidated by the calculation of partial equilibrium species and thermal analysis. A metal screen filter with 500 mesh was employed to dilute the number concentration of the sprayed droplets. The Reynold’s number of the aerosol fluid was kept at the value of 1,200 to keep a short residence time and a laminar flow.

Abstract: An innovative process for synthesising bulk materials using particles has been developed. The process is termed back pressure equal channel angular consolidation (BP-ECAC). Aluminium based materials were successfully consolidated into bulk materials using particles from nano to micro scales. BP-ECAC allowed the particles to be used directly without pre-compacting and casing and the processing temperatures to be significantly lower than those used in conventional sintering. Fully dense bulk samples were obtained instantaneously as the particles were forced to pass the shearing zone under pressure. Nanostructured materials were obtained from the nanometre-sized Al particles. Significant strengthening of the consolidated materials were observed. The new process is promising in producing porosity free, large volume materials with special compositions and structures.

Abstract: The microstructure in heavily deformed metals can be characterized as a complex “mixture” of low and high angle boundaries. By careful annealing of such cold deformed conditions, ultra-fine grained materials can be obtained. This phenomenon has been known for long and utilised in the production of special aluminium sheet qualities, and has received new interest with the emergence of the equal channel angular pressing (ECAP) technique. This work reviews the mechanical properties resulting from plastic deformation and annealing of aluminium, looking at alloys which prior to annealing was subjected to both severe plastic deformation (ECAP) and more conventional deformation by cold rolling. The effect of the resulting microstructures on the subsequent work hardening properties are model, applying the new microstructural metal plasticity model (MMP-model) developed in Trondheim over the last decade.

Abstract: Nanocrystalline nickel powders were prepared by chemical reduction of nickel chloride hydrate with different surfactant at moderate temperature in a pressurized vessel. Nickel nanosheets were generated successfully through reducing the nickel ion complexes, formed by sodium tartrate, at alkaline condition by hydrazine hydrate. The nanosheets and nanowires were characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS) and a high sensitive magnetometer (HSM).

Abstract: Pure aluminium and titanium powders were successfully synthesised into bulk materials using equal channel angular (ECA) consolidation. Powders were used directly without the need to cold-compact them into green bodies. The processing temperatures were significantly lower than the usual sintering temperatures for aluminium and titanium. Fully dense bulk samples were achieved after one pass of ECA deformation through a 90 degree die. Mechanical properties of the as-ECA processed materials were comparable to those of wrought aluminium and titanium through ingot metallurgy. Multiple passes of ECA deformation resulted in refined microstructure and improved mechanical properties. The new process has many advantages over conventional powder sintering and is capable of producing bulk nanomaterials of high integrity.

Abstract: Unidirectional airflow cleanroom was designed to ideally control the flow in order to overcome airborne contamination problems, and that design has not changed much over the past twenty years. However, in reality, it didn’t work as expected. Thus, airborne contamination problems in semiconductor and flat panel display industries still existed even if entire fabrication was processed in unidirectional cleanrooms. Eventually, flow-based re-evaluation of existing unidirectional cleanroom design became inevitable. In this study, we performed fluid dynamics simulations of unidirectional cleanroom at various dimensions, and interpreted the results for further steps of cleanroom designs, such as, inlet/outlet ducts, perforated floors, and equipment arrangement. Furthermore, we developed the mathematical model that interprets the airflow inclination at various cleanroom dimensions into a unified representation to provide designers with concepts for flow-based integration of cleanroom layout. The predicted angle/location of the maximum flow inclination by our mathematical model in terms of fundamental design parameters agreed well with the computational fluid dynamics simulation results and with the expected trends.